Curable resin composition, cured product, flexible printed circuit board, and method for manufacturing the cured product.

Abstract

To provide a curable resin composition that yields a cured product with excellent surface hardness and heat resistance while possessing high flexibility. [Solution] A curable resin composition comprising (a) a (meth)acrylate having 1 to 6 unsaturated groups and not having a urethane bond, (b) a polyfunctional urethane (meth)acrylate, and (c) a photopolymerization initiator, wherein the (c) photopolymerization initiator comprises (c-1) a dialkyl peroxide having a thioxanthone skeleton represented by general formula (1), and the (c-1) component is 0.01 to 15 parts by mass with respect to 100 parts by mass of the total of the (a) component and the (b) component.

Description

[Technical Field]

[0001] The present invention relates to a curable resin composition, a cured product, a flexible printed circuit board, and a method for producing a cured product. [Background technology]

[0002] Traditionally, electronic devices such as smartphones and personal computers have used printed circuit boards (PCBs) equipped with various functional electronic elements. Because PCBs undergo processes such as solder reflow during assembly, their insulating films require high heat resistance; therefore, hardened films cured by light or heat are used. In recent years, with the increasing need for miniaturization and multi-functionality in electronic devices, flexible printed circuit boards (FPCs), which can be bent, have become more common as they allow for high-density component mounting in confined spaces. Surface protection materials for FPCs now require not only high heat resistance but also flexibility.

[0003] To improve flexibility, Patent Document 1 proposes a method of incorporating urethane (meth)acrylate with six or more functional groups into a photosensitive resin composition, while Patent Document 2 proposes a method of incorporating a specific filler. On the other hand, to improve heat resistance, Patent Document 3 proposes a method of improving the crosslinking density of the cured product. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-206992 [Patent Document 2] Japanese Patent Publication No. 2022-017603 [Patent Document 3] Japanese Patent Publication No. 2016-008267 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, heat resistance and flexibility are mutually contradictory properties, and even in the curable resin compositions of the prior art, further improvement is required for the compatibility between the flexibility and heat resistance of the cured film. In Patent Documents 1 and 2, although the flexibility of the cured film is improved, the heat resistance decreases. In Patent Document 3, the crosslink density of the cured product is improved, but the flexibility decreases.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a curable resin composition capable of obtaining a cured product having excellent surface hardness and heat resistance while having high flexibility.

Means for Solving the Problems

[0007] That is, the present invention is a curable resin composition containing (a) a (meth)acrylate having 1 to 6 unsaturated groups and no urethane bond, (b) a polyfunctional urethane (meth)acrylate, and (c) a photopolymerization initiator, wherein the (c) photopolymerization initiator contains (c-1) a general formula (1):

Chemical formula

[0008] Further, in the present invention, the (c) photopolymerization initiator further contains (c-2) a general formula (2):

Chemical formula

[0009] Furthermore, the present invention relates to a cured product obtained from the curable resin composition.

[0010] Furthermore, the present invention relates to a flexible printed wiring board having the cured product.

[0011] Furthermore, the present invention relates to a method for producing a cured product including a step of irradiating the curable resin composition with active energy rays for photocuring.

Effects of the Invention

[0012] The curable resin composition of the present invention can obtain a cured product having excellent surface hardness and heat resistance while having high flexibility.

Modes for Carrying Out the Invention

[0013] <Curable Resin Composition> The curable resin composition of the present invention contains (a) a (meth)acrylate having 1 to 6 unsaturated groups and no urethane bond, (b) a polyfunctional urethane (meth)acrylate, and (c) a photopolymerization initiator.

[0014] <(a) A (meth)acrylate having 1 to 6 unsaturated groups and no urethane bond> The (a) (meth)acrylate having 1 to 6 unsaturated groups and no urethane bond (hereinafter, also simply referred to as the “(a) component”) of the present invention can be used without particular limitation as long as it is a conventionally known one.

[0015] Monofunctional (meth)acrylates having one unsaturated group and no urethane bond include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate; cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, di Ester compounds of (meth)acrylic acid and alicyclic alcohols such as cyclopentenyloxyethyl (meth)acrylate and 2-ethyl-2-adamantyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 3-hydroxy-1-adamantyl (meth)acrylate, hydroxyl-terminated polyethylene glycol mono(meth)acrylate Monomers having hydroxyl groups such as acrylates, hydroxyl-terminated polypropylene glycol mono(meth)acrylates; methoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, 2-phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (3-ethyloxetane-3-yl)methyl (meth)acrylate , monomers having chain-like or cyclic ether links such as cyclic trimethylolpropaneform (meth)acrylate; monomers having nitrogen atoms such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acryloylmorpholine, N-(meth)acryloyloxyethylhexahydrophthalimide;Examples include monomers having an isocyanate group such as 2-(meth)acryloyloxyethyl isocyanate; monomers having an epoxy group such as glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether; monomers having a phosphorus atom such as 2-(meth)acryloyloxy)ethyl phosphate; monomers having a silicon atom such as 3-(meth)acryloxypropyltrimethoxysilane; monomers having a fluorine atom such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3,3-pentafluoropropyl (meth)acrylate, and 2-(perfluorohexyl)ethyl (meth)acrylate; and monomers having a carboxyl group such as (meth)acrylic acid, mono(2-(meth)acryloyloxyethyl) succinate, mono(2-(meth)acryloyloxyethyl) phthalate, mono(2-(meth)acryloyloxyethyl) maleate, and ω-carboxy-polycaprolactone mono(meth)acrylate. Among these, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and phenoxypolyethylene glycol (meth)acrylate are preferred from the viewpoint of being well compatible with components (b) and (c) of the present invention and having excellent curability.

[0016] Polyfunctional (meth)acrylates having 2 to 6 unsaturated groups and no urethane bonds include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, bisphenol F ethylene oxide modified diacrylate, bisphenol A ethylene oxide modified diacrylate, isocyanurate ethylene oxide modified diacrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol di(meth)acrylate monostearate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, Neopentyl glycol di(meth)acrylate hydroxypivalate, glycerin propoxy tri(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 9,9-bis(4-(2-(meth)acryloyloxyethoxy)phenyl)fluorene, 9,9-bis(4-(2-(2-(meth)acryloyl Examples include ester compounds of polyhydric alcohols such as oxyethoxy(ethoxy)phenyl)fluorene and (meth)acrylic acid; bis(4-(meth)acryloxyphenyl) sulfide, bis(4-(meth)acryloylthiophenyl) sulfide, tris(2-(meth)acryloyloxyethyl) isocyanurate, ethylenebis(meth)acrylamide, zinc (meth)acrylate, zirconium (meth)acrylate, epoxy acrylate, polyester acrylate, etc.Among the above, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, bisphenol F ethylene oxide-modified diacrylate, bisphenol A ethylene oxide-modified diacrylate, and isocyanurate ethylene oxide-modified diacrylate are preferred from the viewpoint of imparting flexibility. (a) (meth)acrylates having 1 to 6 unsaturated groups and not having urethane bonds may be used individually or two or more may be mixed in any combination and ratio.

[0017] <(b) Polyfunctional urethane (meth)acrylate> The (b) polyfunctional urethane (meth)acrylate of the present invention (hereinafter also simply referred to as "urethane (meth)acrylate" or "component (b)") is a compound having a urethane bond and two or more radical polymerizable functional groups, such as ethylenically unsaturated groups, within its molecule. Urethane acrylate can be obtained, for example, by reacting a polyhydric alcohol with a polyisocyanate such as isocyanate or isocyanurate and a monofunctional (meth)acrylic monomer having a hydroxyl group.

[0018] Examples of polyhydric alcohols used as raw materials for urethane acrylates include 1,3-butanediol, 1,4-butanediol, trimethylolethane, trimethylolpropane, ditrimethylolethane, ditrimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, diglycerol, glycerin, and numerous other diols such as polysiloxane polyols, poly(oxyalkylene) polyols, polyester polyols, polyether polyols, polyether polyester polyols, polyolefin polyols, poly(alkyl acrylate) polyols, and polycarbonate polyols.

[0019] Examples of isocyanates or polyisocyanates used as raw materials for urethane acrylates include tetramethylene diisocyanate, hexamethylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 3,3-dimethyl-4,4-diphenylene isocyanate, isophorone diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, 1,3-bis(α,α-dimethylisocyanate methyl)benzene, trimethylhexamethylene diisocyanate, and hydrogenated xylylene diisocyanate.

[0020] Examples of monofunctional (meth)acrylic monomers having hydroxyl groups that can be used as raw materials for urethane acrylates include trimethylolpropane diacrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, 5-hydroxycyclooctyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, and oxyethyl di(meth)acrylate isocyanurate.

[0021] (b) The number of functional groups in the polyfunctional urethane (meth)acrylate is preferably 2 to 7. It has good curability and heat resistance, and can also improve flexibility.

[0022] (b) The content of component (a) is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass, in the total of component (a) and component (b), from the viewpoint of the viscosity of the composition before curing and the flexibility after curing.

[0023] <(c) Photopolymerization initiator> The (c) photopolymerization initiator of the present invention comprises (c-1) a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1) (hereinafter also simply referred to as "component (c-1)"). [ka] (In general formula (1), R 1 , R 2 , R 3 and R 4 R independently represents a methyl group or an ethyl group. 5 R represents an alkyl group with 1 to 6 carbon atoms, or a phenyl group. 6 (where n is an independent substituent, representing an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n is an integer from 0 to 2.)

[0024] In general formula (1), R 1 , R 2 , R 3 and R 4 Each of these independently represents a methyl group or an ethyl group. In the present invention, from the viewpoint of improving the stability of dialkyl peroxides having a thioxanthone skeleton represented by general formula (1), R 1 , R 2 , R 3 and R 4 It is preferable that all of these are methyl groups.

[0025] In general formula (1), R 5 R is an alkyl group having 1 to 6 carbon atoms, or a phenyl group. The alkyl group may be linear or branched. 5 Specific examples include methyl group, ethyl group, propyl group, 2,2-dimethylpropyl group, and phenyl group. Among these, R is considered to be the easiest to synthesize thioxanthone derivatives having peroxide bonds. 5 It is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably one selected from a methyl group, an ethyl group, and a propyl group. From the viewpoint of efficiently absorbing light, R 5 It is more preferable that the group is a methyl group or an ethyl group.

[0026] In general formula (1), the substitution position of the dialkylperoxide relative to the thioxanthone is not particularly limited, but from the viewpoint of efficiently converting light energy into thermal energy, it is preferable that it is substituted at the 2nd, 3rd, or 4th position of the thioxanthone skeleton, and from the viewpoint of ease of synthesis, it is more preferable that it is substituted at the 2nd or 3rd position of the thioxanthone skeleton.

[0027] In general formula (1), R 6 The substituents are independent substituents, representing C1-C4 alkyl groups, C1-C4 alkoxy groups, or chlorine atoms. These substituents improve the light absorption characteristics of dialkyl peroxides having a thioxanthone skeleton through a push-pull effect with respect to the emission wavelength of the light source used, allowing for efficient light absorption.

[0028] In general formula (1), n ​​represents an integer from 0 to 2, but from the viewpoint of easily synthesizing dialkylperoxides having a thioxanthone skeleton, n is preferably an integer from 0 to 1, and more preferably 0.

[0029] In general formula (1), when n is an integer from 1 to 2, R 6 The substitution position is not particularly limited, but from the viewpoint of efficiently absorbing light, it is preferably at the 6th or 7th position of the thioxanthone skeleton, and from the viewpoint of easily synthesizing dialkylperoxides having a thioxanthone skeleton, it is more preferably at the 7th position of the thioxanthone skeleton.

[0030] R 6 Specific examples include alkyl groups such as methyl, ethyl, isopropyl, and n-butyl groups; alkoxy groups such as methoxy, ethoxy, n-propyloxy, sec-butyloxy, and tert-butyloxy groups; and chlorine atoms. Among these, R is considered to be the most efficient at absorbing light. 6 It is more preferable that the group is a methoxy group or an ethoxy group.

[0031] The amount of component (c-1) is 0.01 to 15 parts by mass per 100 parts by mass of the total of components (a) and (b). From the viewpoint of curability and heat resistance, the amount of component (c-1) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the total of components (a) and (b). From the viewpoint of flexibility, the amount is preferably 12 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the total of components (a) and (b). Component (c-1) may be used alone or in combination of two or more types.

[0032] Furthermore, the (c) photopolymerization initiator of the present invention may further contain (c-2) a hydroperoxide having a thioxanthone skeleton represented by the following general formula (2) (hereinafter also simply referred to as "component (c-2)"). [ka] (In formula (2), R 1 , and R 2 R independently represents a methyl group or an ethyl group. 3 (where n is an independent substituent, representing an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n is an integer from 0 to 2.)

[0033] In general formula (2), R 1 , and R 2 R independently represents a methyl group or an ethyl group. 1 , R 2 Because the hydroperoxide having the thioxanthone skeleton has a high decomposition temperature, a methyl group is preferred from the viewpoint of improving the storage stability of the polymerizable composition.

[0034] In general formula (2), R 3The substituents are independent and represent an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom. The light absorption characteristics of the hydroperoxide having the thioxanthone skeleton can be adjusted by the push-pull effect of these substituents with respect to the emission wavelength of the lamp used, allowing for efficient absorption of the irradiated light.

[0035] In general formula (2), n represents an integer from 0 to 2. From the viewpoint of facilitating the synthesis of the hydroperoxide having the thioxanthone skeleton, n is preferably an integer from 0 to 1, and more preferably 0.

[0036] In general formula (2), when n is an integer from 1 to 2, the above R 3 The substitution position is not particularly limited, but it is preferable that the substitution is at the 6th or 7th position of the thioxanthone skeleton from the viewpoint of high sensitivity to lamp light, and it is more preferable that the substitution is at the 7th position of the thioxanthone skeleton from the viewpoint of facilitating the synthesis of hydroperoxides having the thioxanthone skeleton.

[0037] R 3 Specific examples include alkyl groups such as methyl, ethyl, isopropyl, and n-butyl groups; alkoxy groups such as methoxy, ethoxy, n-propyloxy, sec-butyloxy, and tert-butyloxy groups; and chlorine atoms. Methoxy and ethoxy groups are more preferable from the viewpoint of efficiently absorbing irradiated light.

[0038] When component (c-2) is included, the proportion of component (c-2) in the total of component (c-1) and component (c-2) is preferably 30% by mass or less, from the viewpoint of preventing curing defects during photocuring and ensuring excellent storage stability of the curable resin composition, preferably 0.1% by mass or more, and more preferably 0.5% by mass or more. (Component (c-2) may be used alone or in combination of two or more types.)

[0039] Furthermore, in the present invention, by using other polymerization initiators in addition to components (c-1) and (c-2) as photopolymerization initiators, the surface curability, deep curability, etc., of the curable resin composition can be improved. When selecting other polymerization initiators, considerations include (a) (meth)acrylates having 1 to 6 unsaturated bonds, (b) polyfunctional urethane (meth)acrylates, other types of additives, the thickness of the cured film, etc.

[0040] Other known polymerization initiators can be used. For example, α-hydroxyacetophenone derivatives such as 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methylpropiophenone, 4'-(2-hydroxyethoxy)-2-hydroxy-2-methylpropiophenone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one; 2-methyl-4'-methylthio-2-morpholinopropiophenone, 2-benzyl-2-(N,N-dimethylamino)-1-(4-morpholino Alpha-aminoacetophenone derivatives such as phenyl)butan-1-one and 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one; acylphosphine oxide derivatives such as diphenyl-2,4,6-trimethylbenzoylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and ethyl(mesitylcarbonyl)phenylphosphineate; 1-[4-(phenylthio)phenyl]octane-1,2-dione-2-(O-benzoyloxy Oxime ester derivatives such as 1-[({1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]ethylidene}amino)oxy]ethanone; halomethyltriazine derivatives such as 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-(3,4-dimethoxystyryl)-4,6-bis(trichloromethyl)1,3,5-triazine, and 2-(4-ethoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine; 2,2-dimethyl Benzyl ketal derivatives such as toxic-2-phenylacetophenone; thioxanthone derivatives such as isopropylthioxanthone; benzophenone derivatives such as 4-(4-methylphenylthio)benzophenone; coumarin derivatives such as 3-benzoyl-7-diethylaminocoumarin and 3,3'-carbonylbis(7-diethylaminocoumarin); imidazole derivatives such as 2-(2-chlorophenyl)-1-[2-(2-chlorophenyl)-4,5-diphenyl-1,3-diazole-2-yl]-4,5-diphenylimidazole;Examples include organic peroxides such as 3,3',4,4'-tetrakis(tert-butylperoxycarbonyl)benzophenone and dibenzoyl peroxide; azo compounds such as azobisisobutyronitrile; and camphorquinone. Other polymerization initiators may be used alone or in combination of two or more.

[0041] <Solvent> The curable resin composition may have additional solvents added to improve viscosity, paintability, and the smoothness of the cured film. These solvents are used to ensure handling and workability during molding of the curable resin composition, and there are no particular restrictions on the amount used.

[0042] Examples of solvents include acetone, methyl ethyl ketone, toluene, xylene, methyl isobutyl ketone, ethyl acetate, ethylene glycol monomethyl ether, N,N-dimethylformamide, N,N-dimethylacetamide, methanol, and ethanol. The solvent may be used alone or in combination of two or more types.

[0043] <Epoxy resin> The curable resin composition may further contain epoxy resin to improve the heat resistance and physical strength of the cured product. The epoxy resin is not particularly limited as long as it has one or more epoxy groups in its molecule; conventionally known epoxy resins can be used. Examples of compounds having one or more epoxy groups in their molecule include bisphenol A type epoxy resins derived from bisphenol A and epichlorohydrin, bisphenol F type epoxy resins derived from bisphenol F and epichlorohydrin, bisphenol S type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, bisphenol F novolac type epoxy resins, alicyclic epoxy resins, diphenyl ether type epoxy resins, hydroquinone type epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, fluorene type epoxy resins, polyfunctional epoxy resins such as trifunctional and tetrafunctional epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, hydantoin type epoxy resins, isocyanurate type epoxy resins, and aliphatic chain epoxy resins. These epoxy resins may be halogenated or hydrogenated. These epoxy resins may be used individually or in combination of two or more types.

[0044] When using epoxy resin, the epoxy resin is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and more preferably 50 parts by mass or less, and more preferably 30 parts by mass or less, relative to 100 parts by mass of the total of components (a) and (b), from the viewpoint of heat resistance and the physical strength of the cured product.

[0045] <Other additives, etc.> The curable resin composition may optionally contain known additives such as sensitizers, thermosetting agents, crosslinking agents, crosslinking accelerators, silane coupling agents, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), antioxidants, fillers, colorants (pigments, dyes, etc.), UV absorbers, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, thickeners, flame retardants, inorganic compounds, and electromagnetic wave absorbing fillers, either individually or in combination of two or more, as long as they do not impair the properties of this embodiment.

[0046] <Method for preparing a curable resin composition> The method for preparing the curable resin composition is not particularly limited. The above components may be mixed in predetermined proportions and then mixed according to conventional methods using a paint shaker, bead mill, sand grind mill, ball mill, attritor mill, two-roll mill, three-roll mill, etc.

[0047] <Method for manufacturing hardened products> The present invention's method for producing a cured product includes the step of irradiating a curable resin composition with active energy rays to photocur it.

[0048] The coating method for the curable resin composition can be any known coating method, and the method for photocuring the curable resin composition is not particularly limited, but it is preferable to irradiate it with active energy rays such as electron beams, ultraviolet rays, visible light, or radiation. The exposure amount of the active energy rays can be appropriately set according to the wavelength and intensity of the active energy rays, the composition of the curable resin composition, and the film thickness. As an example, the exposure amount in the UV-A region is 10 to 5,000 mJ / cm². 2 Preferably, the concentration is 50-3,000 mJ / cm². 2 It is more preferable that this is the case. In addition, a heating step may be performed before or after the step of irradiation with active energy rays.

[0049] The curable resin composition of the present invention is particularly suitable as a solder resist or interlayer insulating film material for flexible printed circuit boards due to its excellent heat resistance and flexibility. The flexible printed circuit board has the cured product of the present invention. [Examples]

[0050] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples.

[0051] <Preparation of curable resin composition> Each component was mixed in the proportions shown in Table 1 to obtain the curable resin compositions of Examples 1-12 and Comparative Examples 1-3. These curable resin compositions were evaluated according to the following method.

[0052] [Evaluation Method] (curable) The curable resin composition obtained above was coated onto an easily adhesive treated PET film (Cosmoshine A4300, manufactured by Toyobo) using a bar coater to create a uniform coating film with a thickness of approximately 30 μm. Next, an illuminance of 4.0 W / cm² was applied using a 385 nm LED light source. 2 Light irradiation was performed at a line speed of 6 m / min. The cured surface was palpated, and the number of irradiations required until the curable resin composition no longer stuck to the hand was evaluated as curability.

[0053] (Flexibility) The curable resin composition prepared above was injected into a glass plate with a 0.5 mm thick spacer in between, and an illuminance of 4.0 W / cm² was applied using a 385 nm LED light source. 2 A cured film was obtained by light irradiation under the conditions of a line speed of 6 m / min and 3 irradiation cycles. The obtained cured film was wrapped around SUS rods with diameters of 10 mm and 15 mm, and the change in appearance was evaluated visually according to the following criteria. An evaluation of ◎ or ○ is considered a pass, with ◎ being more preferable. ◎: No cracks were found in the hardened film wrapped around 10mm and 15mm diameter stainless steel rods. ○: Cracks were observed in the hardened film wrapped around a 10mm diameter stainless steel rod, but no cracks were found in the hardened film wrapped around a 15mm diameter stainless steel rod. ×: Cracks were found in the hardened film wrapped around SUS rods with diameters of 10 mm and 15 mm.

[0054] (Surface hardness (pencil hardness)) The curable resin composition obtained above was coated onto an easily adhesive treated PET film (Cosmoshine A4300, manufactured by Toyobo) using a bar coater to create a uniform coating film with a thickness of approximately 30 μm. Next, an illuminance of 4.0 W / cm² was applied using a 385 nm LED light source. 2 A cured film was obtained by light irradiation under the conditions of a line speed of 6 m / min and 3 irradiations. In accordance with JIS K5600, the fully cured film was scratched with a pencil at a 45° angle with a load of 750 g applied for approximately 10 mm, and the hardest pencil that did not leave a scratch was defined as the pencil hardness. The evaluation criteria for pencil hardness are as follows: An evaluation of ◎ or ○ is considered a pass, with ◎ being more preferable. ◎: The pencil has a hardness of 2H or higher. ○: The pencil hardness is H. ×: The pencil hardness is less than H.

[0055] (Heat resistance) The curable resin composition obtained above was used to create a uniform coating film approximately 30 μm thick on a release-treated PET film (TD06UV0145, manufactured by TOMOEGAWA) using a bar coater. Next, a 385 nm LED light source was used to create an illuminance of 4.0 W / cm². 2 A cured film was obtained by light irradiation under the conditions of a line speed of 6 m / min and 3 irradiation cycles. The cured film was peeled off the release film and the weight loss rate at 300°C was evaluated by measurement under the following conditions. An evaluation of ◎ or ○ is considered a pass, with ◎ being more preferable. Measurement temperature: 30~800℃ Heating rate: 30℃ / min Nitrogen gas: 100 mL / min ◎: Weight reduction rate is 2% or less. ○: The weight reduction rate is between 2% and 5%. ×: The weight reduction rate is more than 5%.

[0056] (Storage stability) The curable resin composition prepared above was placed in a brown glass bottle, shielded from light with aluminum foil, and then left to stand in a constant temperature incubator at 60°C, simulating transport and storage conditions. After standing for a predetermined period, the change in the appearance of the curable resin composition was visually evaluated according to the following criteria: "◎" if no gelation was visually observed after 3 months of storage, "○" if no gelation was visually observed after 2 months of storage, and "×" if gelation was visually observed after 2 months of storage. Gelation refers to a state in which the composition does not flow when the container is tilted. In the evaluation, "◎" or "○" is considered a pass, with "◎" being more preferable. ◎: No gelation was observed visually after 3 months of storage. ○: No gelation was observed visually after 2 months of storage. ×: After 2 months of storage, gelation was visually confirmed.

[0057] Further details regarding the abbreviations and other terms listed in Table 1 are as follows: IBXA: Isobornyl acrylate (manufactured by Osaka Organic Chemical Co., Ltd.) M-225PPGDA: Polypropylene glycol diacrylate (manufactured by Toagosei) A-TMPT: Trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) UV-3700B: Bifunctional urethane acrylate (manufactured by Mitsubishi Chemical) UV-6300B: Heptafunctional urethane acrylate (manufactured by Mitsubishi Chemical) TPO: Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (manufactured by IGM Resins BV) jER828: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical) DICY-7: Dicyandiamide (manufactured by Mitsubishi Chemical) Compounds 1, 2, 10, and 11, listed in Table 1, were synthesized according to the method described in International Publication No. 2023 / 190161. Details of compounds 1, 2, 10, and 11 are shown in Table 2.

[0058] [Table 1]

[0059] [Table 2]

[0060] As shown in Table 1, the curable resin compositions of each example exhibited good curability, hardness, and heat resistance, as well as excellent flexibility. On the other hand, the compositions of each comparative example showed insufficient curability or inferior flexibility and heat resistance.

Claims

1. A curable resin composition comprising (a) a (meth)acrylate having 1 to 6 unsaturated groups and no urethane bonds, (b) a polyfunctional urethane (meth)acrylate, and (c) a photopolymerization initiator, The (c) photopolymerization initiator is (c-1) general formula (1): 【Chemistry 1】 (In general formula (1), R １ , R ２ , R ３ and R ４ Each of these independently represents either a methyl group or an ethyl group, R ５ R represents an alkyl group or phenyl group having 1 to 6 carbon atoms. ６ The compound comprises a dialkyl peroxide having a thioxanthone skeleton represented by ), where is an independent substituent, representing an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n represents an integer from 0 to 2. The curable resin composition is characterized in that the (c-1) component is present in an amount of 0.01 to 15 parts by mass with respect to 100 parts by mass of the sum of the (a) component and the (b) component.

2. The (c) photopolymerization initiator further comprises (c-2) general formula (2): 【Chemistry 2】 (In general formula (2), R １ , and R ２ independently represent a methyl group or an ethyl group, and R ３ is an independent substituent and represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n represents an integer from 0 to 2.) containing a hydroperoxide having a thioxanthone skeleton represented by The curable resin composition according to claim 1, characterized in that the proportion of component (c-2) in the total of component (c-1) and component (c-2) is 30% by mass or less.

3. A cured product characterized by being obtained from the curable resin composition described in claim 1 or 2.

4. A flexible printed circuit board characterized by having the cured product described in claim 3.

5. A method for producing a cured product, characterized by comprising the step of irradiating the curable resin composition according to claim 1 or 2 with active energy rays to photocur it.

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